Protein kinase C (PKC) is a superfamily of lipid-activated Ser/Thr kinases involved in multiple signal transduction pathways. There are thirteen PKC-isoforms that have been identified and are classified according to their regulation by cellular signaling molecules such as diacylglycerol, phospholipids, and calcium. The protein kinase C isozymes, alpha, beta (two splice variants PKCβI and PKCβII) and gamma, require membrane phospholipids, calcium and diacylglycerolphorbol esters for full activation. The delta, epsilon, eta, and theta forms of PKC are calcium-independent in their mode of activation. The zeta and lambda forms of PKC are independent of both calcium and diacylglycerol and are believed to require only membrane phospholipids for their activation.
The tissue-specific expression and activation of PKC-isoforms suggests that individual PKC-isoforms might be potential therapeutic targets. For diabetes, activation of PKC-beta has been demonstrated in tissues of diabetic animals and has been implicated in the development of microvascular abnormalities related to the hyperglycemic state. Genetic polymorphisms have been identified in the 5′-flanking upstream region of the PKCβ gene in Japanese patients with type II diabetes. This PKCβ genetic variation was associated with a significant increase in the susceptibility to develop diabetic vascular complications and macrovascular diseases such as coronary heart disease.
In a large case-control study at the Joslin Diabetes Center, additional polymorphisms were identified in the PKCβ promoter region that had an association with type I diabetes mellitus (duration<24 years) and a greater risk for development of diabetic nephropathy. Administration of PKCβ inhibitors such as ruboxistaurin mesylate (LY333531, Lilly) in diabetic animal models, was shown to prevent or ameliorate the hemodynamic changes and vascular damage associated with diabetic nephropathy, diabetic peripheral neuropathy, and diabetic retinopathy. Way, K. J. et al, Diabet. Med. 18: 945-959 (2001); Vinik, A., Expert Opin. Investig. Drugs 14: 1547-1559 (2005). Together with additional data from phase II and phase III clinical studies of ruboxistaurin mesylate for treatment of diabetes and diabetic microvascular complications, there is a building body of evidence to support the rationale that PKCβ can function as a molecular target for diabetic complications and for the development of selective-PKCβ inhibitors as potential therapeutic agents.
The compounds of the present invention are protein kinase C beta II inhibitors, and are therefore believed to be useful in the treatment of conditions associated with diabetes mellitus and its complications, cancer, ischemia, inflammation, central nervous system disorders, cardiovascular disease and dermatological disease.